Lithographic apparatus, device manufacturing method and computer program product

Abstract

In a lithographic apparatus, a corrective irradiation procedure is performed using an illumination mode arranged so as to heat a selected part of an element of the projection system near a pupil plane thereof that is relatively unheated during production exposure. The corrective irradiation procedure aims to improve uniformity of optical element heating of the projective system and/or to reduce a phase gradient.

1. A lithographic apparatus comprising:
 an illumination system configured to condition a radiation beam so as to illuminate a patterning device in a first or a second illumination mode selectively; 
 a support structure constructed to support the patterning device, the patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned beam; 
 a substrate table constructed to hold a substrate; 
 a projection system configured to project the patterned beam onto a target portion of the substrate, the projection system comprising a plurality of optical elements and having a pupil plane, at least one of the optical elements being located in or near the pupil plane; and 
 a control system configured to control the illumination system, the support structure and the substrate table to select the first illumination mode when a pattern on the patterning device and a substrate on the substrate table are in the path of the radiation beam to perform a production exposure and to select the second illumination mode during a time that no substrate is in the path of the radiation beam to perform a corrective irradiation process, 
 wherein, in the first illumination mode, an angular distribution of radiation at the patterning device is such that an intensity of the patterned beam is substantially contained within a first part of the cross-sectional area of the at least one optical element and within a second part of the cross-sectional area of the at least one optical element in the second illumination mode, the first and second parts being substantially non-overlapping and the combination of the first and second parts not encompassing the entire cross-sectional area of the at least one optical element, 
 wherein elements of the lithographic apparatus are constructed and arranged such that an intensity distribution of the patterned beam in the second illumination mode results in an optical element heating effect that causes the at least one optical element that is non-uniformly heated in the first illumination mode to be heated substantially uniformly thereby correcting any optical aberrations caused by the non-uniform heating. 
 
     
     
       2. The apparatus of  claim 1 , wherein the lithographic apparatus includes an exchange mechanism to selectively position a first diffractive optical element or a second diffractive optical element in the path of the radiation beam to effect the first or second illumination modes respectively. 
     
     
       3. The apparatus of  claim 1 , wherein the lithographic apparatus includes a first diffractive optical element in the path of the radiation beam, the first diffractive optical element being arranged to effect the first illumination mode, and an insertion mechanism arranged to selectively position a second diffractive optical element in the path of the radiation beam, the second diffractive element being arranged to effect the second illumination mode in combination with the first diffractive optical element. 
     
     
       4. The apparatus of  claim 3  wherein the lithographic apparatus includes an exchange mechanism arranged to selectively insert into the path of the radiation beam one of a plurality of first diffractive optical elements, each first diffractive optical element being arranged to effect a different first illumination mode and wherein the second diffractive element is arranged to effect the second illumination mode in combination with any one of the first diffractive optical elements. 
     
     
       5. The apparatus of  claim 1 , wherein the control system is further configured to control a radiation source to emit the radiation beam at a first power level or a second power level respectively when the first or second illumination modes is selected, the second power level being higher than the first power level. 
     
     
       6. The apparatus of  claim 1 , wherein the second part is arranged so that the corrective irradiation procedure is effective to reduce aberrations caused by non-uniform heating in the production exposure of the at least one optical element. 
     
     
       7. The apparatus of  claim 1 , wherein first illumination mode is characterized by a dipole radiation distribution and the second illumination mode is characterized by a quadrupole radiation distribution having poles adjacent the locations of the poles of the first illumination mode. 
     
     
       8. The apparatus of  claim 7 , wherein the poles of the dipole distribution are segments of an annulus and the poles of the quadrupole distribution are segments of the same annulus. 
     
     
       9. The apparatus of  claim 1 , wherein the combination of the first and second illumination modes would be such as to give rise to a heating effect in the projection system that does not cause aberrations in the projected patterned beam that are unacceptable. 
     
     
       10. The apparatus of  claim 1 , wherein the projection system further comprises an adjustable optical element configured to correct an aberration in the projected patterned beam and wherein the combination of the first and second illumination modes would be such as to give rise to a heating effect in the projection system that causes aberrations that are correctable by the adjustable optical element. 
     
     
       11. The apparatus of  claim 1 , comprising a setting device configured to direct different parts of the radiation beam prior to the patterning device into different directions to provide a desired intensity distribution of the radiation beam, the setting device including a plurality of directing elements, each directing element configured to be oriented to direct a corresponding part of the radiation beam into a desired direction. 
     
     
       12. A lithographic apparatus comprising:
 an illumination system configured to condition a radiation beam so as to illuminate a patterning device in a first or a second illumination mode selectively, the illumination system comprising 
 a first diffractive optical element in the path of the radiation beam, the first diffractive optical element being arranged to effect the first illumination mode, and a second diffractive optical element in the path of the radiation beam, the second diffractive element being arranged to effect the second illumination mode in combination with the first diffractive optical element, 
 an insertion mechanism arranged to selectively position the second diffractive optical element in the path of the radiation beam; 
 a support structure constructed to support the patterning device, the patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned beam; 
 a substrate table constructed to hold a substrate; 
 a projection system configured to project the patterned beam onto a target portion of the substrate, the projection system comprising a plurality of optical elements and having a pupil plane, at least one of the plurality of optical elements being located in or near the pupil plane; and 
 a control system configured to control the illumination system, the support structure and the substrate table to select the first illumination mode when a pattern on the patterning device and a substrate on the substrate table are in the path of the radiation beam to perform a production exposure and to select the second illumination mode during a time that no substrate is in the path of the radiation beam to perform a corrective irradiation process. 
 
     
     
       13. The lithographic apparatus according to  claim 12 , wherein the first diffractive optical element is configured to form an illumination distribution in the pupil plane, and the second diffractive optical element is configured to affect intensity distribution in the pupil plane. 
     
     
       14. The lithographic apparatus of  claim 12 , wherein, in the first illumination mode, an angular distribution of radiation at the patterning device is such that an intensity of the patterned beam is substantially contained within a first part of the cross-sectional area of the at least one optical element and within a second part of the cross-sectional area of the at least one optical element in the second illumination mode, the first and second parts being substantially non-overlapping and the combination of the first and second parts not encompassing the entire cross-sectional area of the at least one optical element.